#include <stdio.h>
#include <stdlib.h>
#define C 200
char a[C+1],b[C+1];
int main()
{
    short n,i,o,j;
    freopen("nunta.in","r",stdin);
    freopen("nunta.out","w",stdout);
    scanf("%hd",&n);
    for(i=0; i<=C; i++)
        a[i]=b[i]=0;
    a[C]=1;
    b[C]=2;
    for(i=3; i<=n; i++)
    {
        if(!(i%2))
        {
            o=0;
            for(j=C; j>0; j--)
            {
                b[j]+=a[j]+o;
                o=b[j]/10;
                b[j]%=10;
            }
        }
        else
        {
            o=0;
            for(j=C; j>0; j--)
            {
                a[j]+=b[j]+o;
                o=a[j]/10;
                a[j]%=10;
            }
        }
    }
    if(n%2)
    {
        i=0;
        while(a[i]==0)
            i++;
        while(i<=C)
            printf("%d",a[i++]);
    }
    else
    {
        i=0;
        while(b[i]==0)
            i++;
        while(i<=C)
            printf("%d",b[i++]);
    }

    return 0;
}